Mobile communications systems employ duplex technology to provide downlink (DL) and uplink (UL) service. The duplex technology may be largely divided into frequency division duplexing (FDD) and time division duplexing (TDD).
In FDD, frequency band allocated for DL transmission and frequency band allocated for UL transmission are fixed. As the utilization of the frequency band is not variable, it is difficult to efficiently respond to increased DL traffic.
In TDD, on the other hand, the same frequency band may be variably allocated to the downlink (DL) transmission or the uplink (UL) transmission depending on time intervals. A frame may be divided into sub-frames, and each of the sub-frames may be allocated for DL or UL transmission.
Such TDD can change the utilization of the same frequency band depending on time intervals and is evolving toward dynamic TDD (D-TDD) that allows for adaptively responding to DL/UL traffic by way of increasing the number of sub-frames in a frame that are allocated for DL transmission (hereinafter referred to as DL sub-frames) when the amount of DL traffic increases instantaneously while decreasing the number of sub-frames that are allocated for UL transmission (hereinafter referred to as UL sub-frames) according to the number of increased DL sub-frames, for example.
Recently, mobile communications systems install various types of cells such as pico-cells, femtocells and the like and evolve to increase transmission capacity per area by reutilizing frequency. As a result, a number of cells are densely disposed.
As such, in a network environment where a number of cells densely coexist, adjacent cells are very close to one another, and thus interference between adjacent cells becomes strong. In particular, if TDD is employed, there is a difference between the strengths of interference on DL and UL transmissions by an adjacent cells that affect another cell (hereinafter referred to as “DL interference” and “UL interference,” respectively). This is because the DL interference occurs when a base station constantly receiving power transmits data and thus is transmitted at higher transmission power than UL transmission.
In view of the above, the exemplary embodiments of the present disclosure propose an approach to achieve optimal interference control taking into account a different between the DL interference strength and the UL interference strength by an adjacent cell by way of controlling cells based on D-TDD in a network environment where a number of cells employing TDD coexist.